The efficiency of electrophotographic type copiers or printers depends upon the proper relative charge being maintained between a photoconductive imaging member and a developing mechanism. This charge relationship is used to attract toner or other development material from a supply to the photoconductive member in conformance with both the outline and density of the electrostatic image on the photoconductive member. The electrostatic image that undergoes this development is formed by exposing the previously charged photoconductive member to a light image of the original being copied or to exposure by an electro-optical exposure source.
One method of sustaining the proper charge relationship between the photoconductive member and the developing mechanism is to use an electrostatic voltmeter, commonly called an electrometer, to sense potentials on the photoconductive member at some appropriate point. The electrometer""s primary function is to ensure that the desired film voltage is indeed the actual film voltage on the film. To ensure that the photoconductor is charged to the desired film voltage (calculated and set by a densitometer), the electrometer monitors the running average of the actual film voltage. If the film voltage is different from the desired film voltage, the electrometer corrects the grid setting for the primary charger accordingly. The electrometer also monitors the running average of the charging efficiency. The electrometer can be used as a service instrument to provide a visible indication of the photoreceptor charge condition from which the electrostatic development field can be adjusted. In other cases, a feedback loop may be provided as part of process control to enable readings from the electrometer to be used to automatically control the development field.
In these machines, adjustment of one or more of the various operating parameters, such as the primary charge potential level, normally requires that the bias be identified, and changes made therein monitored. Failing to monitor and adjust the bias may result in control of image quality because the proper amount of toner is not used.
In such systems, the charge relationship must be controlled in a dynamic manner. That is, the electrometer must be able to respond within a specified window, in which the voltage measurement is made.
Presently, the current response time of an electrometer is only measured in a static mode. Typically, a one kilovolt signal is applied to a stationary plate and the corresponding electrometer signal is measured using an oscilloscope. Thus, electrometer response currently is measured and specified in a static mode. However, actual use of an electrometer in an electrophotographic system is in a dynamic mode. That is, the electrometer must respond to quickly changing operational parameters, such as a moving photoconductive belt. There is a difference in electrometer response when comparing static versus dynamic and thus static testing may not be sufficient to assure the performance of an electrometer.
It is therefore an object of the present invention to provide a new and improved apparatus and method for determining the response of electrometers used in electrophotographic reproduction machines.
The invention and its various advantages will become more apparent to those skilled in the art from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings.
An apparatus is provided for determining the response of an electrometer used in an electrophotographic recording apparatus. The apparatus includes a movable base disposed adjacent said electrometer. The base includes a non-conductive material. A conductive pattern is disposed on the base. The conductive pattern is electrically connected to a variable power supply. A motor moves or drives the base past the electrometer. The motor is controlled by a motor control to vary the speed of movement of said base.
The present invention also contemplates a method for determining the response of an electrometer used in an electrophotographic recording apparatus. An electrometer to be tested is selected and the operational parameters of the electrometer are dynamically tested. In a preferred embodiment, the dynamically testing is accomplished by providing a movable test pattern adjacent the electrometer, supplying a voltage to the test pattern, and moving said test pattern relative to the electrometer.